24 a/D COnVeRTeR (aDC10)
S1C17624/604/622/602/621 TeChniCal Manual
Seiko epson Corporation
24-5
R
S
: Source impedance
R
AIN
: Analog input resistance
C
AIN
: Analog input capacitance
AV
DD
V
SS
R
AIN
R
S
AIN
x
C
AIN
3.5.1 Equivalent Circuit of Analog Input Portion
Figure 24.
Determine f
ADCLK
and ADST[2:0] settings to satisfy the expression below.
t
ACQ
= 8
×
(R
S
+ R
AIN
)
×
C
AIN
(See “Electrical Characteristics” for the R
AIN
and C
AIN
values.)
1
———
×
(Number of clock cycles set by ADST[2:0]) > t
ACQ
f
ADCLK
f
ADCLK
: A/D conversion clock frequency [Hz]
The following shows the relation between sampling time and sampling rate.
f
ADCLK
Sampling rate [sps] = ————————————————————
Number of clock cycles set by ADST[2:0] + 11
Setting Conversion Result Storing Mode
24.3.6
The A/D converter loads the 10-bit conversion results into ADD[15:0]/ADC10_ADD register (16-bit register) after
an A/D conversion has completed. At this time, the 10-bit conversion results are aligned in the 16-bit register ac-
cording to the conversion result storing mode set with STMD/ADC10_TRG register either as the high-order 10 bits
(left justify mode) or the low-order 10 bits (right justify mode). The remaining six bits are all set to 0.
ADD bit
15
...
10
9
...
6
5
...
0
Left justify mode (STMD = 1) (MSB)
10-bit conversion results
(LSB)
0
...
0
Right justify mode (STMD = 0)
0
...
0
(MSB)
10-bit conversion results
(LSB)
3.6.1 Conversion Data Alignment
Figure 24.
a/D Conversion Control and Operations
24.4
The A/D converter should be controlled in the sequence shown below.
1. Activate the A/D converter.
2. Start A/D conversion.
3. Read the A/D conversion results.
4. Terminate A/D conversion.
activating a/D Converter
24.4.1
After the settings described in Section 24.3 have been completed, write 1 to ADEN/ADC10_CTL register to enable
the A/D converter. The A/D converter is thereby ready to accept a trigger to start A/D conversion. To set up the A/D
converter again, or when the A/D converter is not used, ADEN must be set to 0.
Starting a/D conversion
24.4.2
The A/D converter starts A/D conversion when a trigger is input while ADEN is 1. When software trigger is select-
ed, an A/D conversion starts by writing 1 to ADCTL/ADC10_CTL register.
The A/D converter accepts triggers from only the trigger source selected by ADTS[1:0]/ADC10_TRG register.
Once a trigger is input, the A/D converter starts sampling of the analog input signal and A/D conversion beginning
with the conversion start channel selected by ADCS[2:0]/ADC10_TRG register.
The software trigger bit ADCTL functions as an A/D conversion status bit that goes 1 while A/D conversion is un-
derway even if it has started by another trigger source. The channel in which conversion is underway can be identi-
fied by reading ADICH[2:0]/ADC10_CTL register.